IT systems typically represented by those of the Internet sites are configured by various servers such as WEB servers that display information to users, AP (application) servers that unite and process information, DB (data base) servers that stores information, etc. Those servers use computers, each being configured by a CPU, a memory, I/O devices, etc. Because such an IT system is configured by many servers as described above, there has appeared a blade server recently so as to make it easier to manage those servers. One blade server includes many computers (e.g., as disclosed in the JP-A No. 2002-32153). Furthermore, because there has been realized a CPU that can include plural processor cores (multicore CPU), thereby the CPU processing performance has been improved and accordingly the CPU has come to be used more efficiently, virtual server techniques have also appeared to operate plural virtual servers in one computer.
Computers use I/O devices such as the NIC (Network Interface Card), the FC-HBA (Fiber Channel-Host Bus Adapter), etc. to connect networks and storages for communications. And as described above, if one computer operates plural servers, the number of I/O devices per computer comes often to be short comparatively. In order to solve such a problem, there are some well-known techniques. The multi-route PCI switching technique and the multi-route I/O virtualization technique (IOV IO Virtualization) are typical ones. The multi-route PCI switching technique enables the connection between plural computers and plural PC devices that are I/O devices and the multi-route I/O virtualization technique enables one PCI device to be shared by plural computers. The former multi-route PCI switching technique can change the number of PCI devices connectable to one computer scalably (e.g., U.S. Pat. No. 7,058,738: “Advanced Switching Technology Tech Brief”, issued in 2005, written by ASI-SIG, pages 1 to 2; etc.) The latter multi-route I/O virtualization technique can increase the number of I/O devices virtually by enabling one PC device to be shared among computers. Using those techniques, therefore, can solve the problem of the shortage of I/O devices that might otherwise occur when virtual servers are used.